package ai

import (
	"encoding/json"
	"fmt"
	"slices"

	"github.com/greyson/super-auto-pets-board-game/internal/game"
)

// Memory is the bot's private notebook: everything it has legitimately
// learned from public information, carried between turns (and, serialized
// into the game state, across server restarts). It is the bot's substitute
// for a human player's attention — nothing in here is unavailable to a human
// watching the same screen.
type Memory struct {
	LastSeq         int         `json:"lastSeq"`         // last event-log entry processed
	LastBattleRound int         `json:"lastBattleRound"` // last battle lineup ingested
	PrevShopRow     []game.Card `json:"prevShopRow"`     // shop row at the previous observation
	Opp             OppModel    `json:"opp"`
}

// OppModel is the bot's belief about one opponent's deck. Known holds cards
// it has actually seen there (battle lineups reveal entire decks each round;
// shop buys are public); Hidden counts cards it knows exist but has never
// seen — trade-in picks, whose tier is public but whose identity is not.
type OppModel struct {
	Seat   int          `json:"seat"`
	Known  []game.Card  `json:"known"`
	Hidden []HiddenCard `json:"hidden,omitempty"`
}

// HiddenCard is a card the opponent holds that the bot has not seen. Name is
// set when the card was later named publicly (e.g. a trade pick revealed by
// its buy ability) — the suit still isn't known, but the stats are.
type HiddenCard struct {
	Tier int    `json:"tier"`
	Name string `json:"name,omitempty"`
}

// LoadMemory decodes a bot's stored memory; a nil or corrupt blob yields a
// fresh one (the model self-heals from the next battle lineup anyway).
func LoadMemory(raw json.RawMessage) *Memory {
	m := &Memory{}
	if len(raw) > 0 {
		_ = json.Unmarshal(raw, m)
	}
	return m
}

// Marshal encodes the memory for storage on the bot's Player.
func (m *Memory) Marshal() json.RawMessage {
	raw, err := json.Marshal(m)
	if err != nil {
		return nil
	}
	return raw
}

// Observe updates the memory from the bot's latest view. The server calls
// this on every state change, so consecutive observations are one action
// apart. It reads three public sources, in order:
//
//  1. new event-log entries, whose structured tags describe opponent shop
//     actions (buys name the card, sells name what left, trades list the
//     discarded trio, spawn entries count apples gained);
//  2. the latest battle's lineups, which reveal both decks in full and reset
//     the model to ground truth every round (so any drift lasts one round);
//  3. the opponent's public deck size, as a reconciliation safety net.
func Observe(v *game.View, m *Memory) {
	if v.YouSeat < 0 {
		return
	}
	oppSeat := -1
	for _, p := range v.Players {
		if p.Seat != v.YouSeat {
			oppSeat = p.Seat
			break
		}
	}
	if oppSeat < 0 {
		return
	}
	m.Opp.Seat = oppSeat

	for _, e := range v.Log {
		if e.Seq <= m.LastSeq {
			continue
		}
		m.LastSeq = e.Seq
		if e.Seat != oppSeat {
			continue
		}
		switch {
		case e.Kind == game.LogBuy:
			if c, ok := cardByID(m.PrevShopRow, e.Source); ok {
				m.Opp.Known = append(m.Opp.Known, c)
			} else if c, ok := templateByName(e.CardName); ok {
				m.Opp.Known = append(m.Opp.Known, c)
			}
		case e.Kind == game.LogSell:
			m.removeOppCard(e.Source, e.CardName)
			m.Opp.Known = append(m.Opp.Known, memApple(len(m.Opp.Known)))
		case e.Kind == game.LogTrade:
			for _, id := range e.Cards {
				m.removeOppCard(id, "")
			}
		case e.Kind == game.LogTradePick:
			m.Opp.Hidden = append(m.Opp.Hidden,
				HiddenCard{Tier: min(e.Round+1, game.MaxRounds), Name: e.CardName})
		case e.Spawn == "apple" && e.Kind == "":
			n := max(e.Count, 1)
			for range n {
				m.Opp.Known = append(m.Opp.Known, memApple(len(m.Opp.Known)))
			}
		}
	}

	// Battle lineups are ground truth: rebuild the model from the opponent's
	// revealed deck, minus temporary cards (they expire with the battle).
	if v.Battle != nil && v.Battle.Round > m.LastBattleRound && oppSeat < len(v.Battle.Lineups) {
		m.LastBattleRound = v.Battle.Round
		m.Opp.Known = m.Opp.Known[:0]
		m.Opp.Hidden = nil
		for _, c := range v.Battle.Lineups[oppSeat] {
			if !c.Temporary {
				m.Opp.Known = append(m.Opp.Known, c)
			}
		}
	}

	// Reconcile with the public deck size. Skipped during the battle phase,
	// where the live deck still holds temporaries the model excludes.
	if v.Phase == game.PhaseShop || v.Phase == game.PhaseCleanup || v.Phase == game.PhaseArrange {
		size := v.Players[slices.IndexFunc(v.Players, func(p game.PlayerView) bool { return p.Seat == oppSeat })].DeckSize
		for len(m.Opp.Known)+len(m.Opp.Hidden) < size {
			m.Opp.Hidden = append(m.Opp.Hidden, HiddenCard{Tier: v.Round})
		}
		for len(m.Opp.Known)+len(m.Opp.Hidden) > size {
			if len(m.Opp.Hidden) > 0 {
				m.Opp.Hidden = m.Opp.Hidden[:len(m.Opp.Hidden)-1]
			} else {
				m.Opp.Known = m.Opp.Known[:len(m.Opp.Known)-1]
			}
		}
	}

	m.PrevShopRow = append(m.PrevShopRow[:0], v.ShopRow...)
}

// removeOppCard drops one card from the model: by exact ID when we tracked
// it, by name as a fallback (model-minted apples have synthetic IDs), and
// failing both, one hidden card — something we didn't know they had left.
func (m *Memory) removeOppCard(id, name string) {
	if i := slices.IndexFunc(m.Opp.Known, func(c game.Card) bool { return c.ID == id }); i >= 0 {
		m.Opp.Known = slices.Delete(m.Opp.Known, i, i+1)
		return
	}
	if name != "" {
		if i := slices.IndexFunc(m.Opp.Known, func(c game.Card) bool { return c.Name == name }); i >= 0 {
			m.Opp.Known = slices.Delete(m.Opp.Known, i, i+1)
			return
		}
	}
	if len(m.Opp.Hidden) > 0 {
		m.Opp.Hidden = m.Opp.Hidden[:len(m.Opp.Hidden)-1]
	}
}

func cardByID(cards []game.Card, id string) (game.Card, bool) {
	if id == "" {
		return game.Card{}, false
	}
	for _, c := range cards {
		if c.ID == id {
			return c, true
		}
	}
	return game.Card{}, false
}

// templateByName mints a reference copy of a named card from the printed
// tier contents. The suit is whatever the first printed copy has — callers
// only rely on stats and effects.
func templateByName(name string) (game.Card, bool) {
	if name == "" {
		return game.Card{}, false
	}
	for tier := 1; tier <= game.MaxRounds; tier++ {
		for _, c := range game.TierContents(tier) {
			if c.Name == name {
				return c, true
			}
		}
	}
	return game.Card{}, false
}

// memApple mints an apple for the opponent model. The ID is synthetic — it
// only needs to not collide with real card IDs.
func memApple(n int) game.Card {
	return game.Card{
		ID:        fmt.Sprintf("mem-apple-%d", n),
		Kind:      game.KindFood,
		Name:      "Apple",
		Food:      game.FoodApple,
		Temporary: true,
	}
}